A method for preparing a lithium battery solid-state electrolyte

Abstract

The application relates to the technical field of solid-state lithium batteries, in particular to a preparation method of a lithium battery solid-state electrolyte, which comprises the following steps: mixing ammonium fluoride and LLZTO powder without surface treatment in a preset molar ratio under preset mixing conditions; determining whether the mixing is uniform based on the mixing homogeneity of the mixed LLZTO, and determining the adjustment of the mixing speed according to the difference between the mixing homogeneity and a preset mixing homogeneity; putting the mixed LLZTO into a reaction container, the reaction container is used to heat the reaction temperature to a preset decomposition temperature at a preset heating rate, and then the reaction temperature is kept for a preset decomposition time; screening the LLZTO with a surface covered with a LiF layer obtained after the reaction container is cooled at a preset cooling temperature and a preset pressure relief pressure under the protection of an inert atmosphere; determining the eligibility of the side reaction inhibition based on the reaction deviation index of the LLZTO with the surface covered with the LiF layer, and determining the adjustment of the preset heating rate according to the ratio of the reaction deviation index threshold value and the reaction deviation index, and the application improves the Li2CO3 removal efficiency of the LLZTO surface.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state lithium batteries, and in particular to a method for preparing a solid-state electrolyte for a lithium battery. Background Art

[0002] Solid electrolytes have emerged to address the leakage and flammability issues inherent in liquid electrolytes. Since LLZTO (Lysine Fluoride) is a novel garnet-type ceramic nanoparticle, removing Li₂CO₃ (Li₂CO₃) generated on the surface of LLZTO electrolytes during preparation and storage is a key step in their industrialization. Traditional mechanical polishing cannot completely remove Li₂CO₃ from the LLZTO surface and may introduce other impurities, damaging the electrolyte structure. High-temperature heat treatment consumes significant energy and results in lithium loss, leading to low Li₁ conductivity. Using strong acids such as HCl to treat the surface reaction is difficult to precisely control, and aqueous acid treatment is detrimental to water-sensitive garnet solid electrolytes, resulting in low ionic conductivity. Using hydrogen fluoride gas to remove LLZTO is a simple process, but hydrofluoric acid is primarily produced from fluorite, a non-renewable resource. With the rapid development of the fluorine chemical industry, my country faces a shortage of fluorite resources. Furthermore, the cost of producing LLZTO using HF gas is prohibitive. Therefore, it is necessary to develop a low-cost, efficient solution for removing Li₂CO₃ from the LLZTO surface.

[0003] Chinese patent application publication number: CN112072168A discloses a semi-solid lithium battery electrolyte and a preparation method, which includes the following processes: (1) mixing a mixture slurry of lithium chloride, yttrium chloride, doping phase M and anhydrous ethanol with a binder and a foaming agent, pressing and molding, and sintering to obtain a porous electrolyte membrane; (2) first immersing the porous electrolyte membrane in an ethylene glycol solution of aminosulfonic acid, then adding allyl polyethylene glycol monoether and urea, heating the reaction under inert gas protection, then adding acrylic acid to cool the reaction, and then continuing to add calcium chloride to stand for reaction, and finally taking the electrolyte membrane out of the oven for drying and subsequent processing to obtain a semi-solid lithium battery electrolyte.

[0004] However, the prior art has the following problems: the prior art does not mix solid ammonium fluoride with LLZTO, resulting in low ionic conductivity of LLZTO, thereby leading to low Li2CO3 removal efficiency on the surface of LLZTO. Summary of the Invention

[0005] To this end, the present invention provides a method for preparing a solid electrolyte for a lithium battery, so as to overcome the problem that the prior art does not mix solid ammonium fluoride with LLZTO, resulting in low ionic conductivity of LLZTO and thus low Li2CO3 removal efficiency on the LLZTO surface.

[0006] To achieve the above object, the present invention provides a method for preparing a solid electrolyte for a lithium battery, comprising:

[0007] Mixing ammonium fluoride and LLZTO powder that has not been surface treated at a preset molar ratio under preset mixing conditions to obtain mixed LLZTO;

[0008] determining whether the mixing is uniform based on the mixing homogeneity of the mixed LLZTO, and adjusting the mixing rate according to the difference between the mixing homogeneity and a preset mixing homogeneity;

[0009] The uniformly mixed LLZTO is placed in a reaction container, and the reaction temperature of the reaction container is increased to a preset decomposition temperature at a preset heating rate and then maintained for a preset decomposition time;

[0010] Screening the LLZTO with a surface covered with a LiF layer obtained after the reaction container is cooled to a preset temperature and released at a preset pressure under inert atmosphere;

[0011] Determining the eligibility of side reaction suppression based on the reaction deviation index of the LLZTO having the LiF layer on the surface, and adjusting the preset heating rate according to the ratio of the reaction deviation index threshold to the reaction deviation index;

[0012] Under the condition that the side reaction is suppressed to a qualified level, the LLZTO composite electrolyte is prepared.

[0013] Furthermore, the preset molar ratio of ammonium fluoride:LLZTO powder is x:1, wherein x is 0.05 to 0.1, and the preset mixing conditions include a mixing speed and a mixing time, wherein the mixing speed ranges from 200 rpm to 500 rpm, and the mixing time ranges from 30 min to 60 min.

[0014] Furthermore, the preset heating rate range is 5°C / min to 10°C / min, the preset decomposition temperature range is 180°C to 220°C, and the preset decomposition time range is 1.2h to 1.5h.

[0015] Furthermore, the preset cooling temperature is 25°C to 30°C, and the preset pressure relief pressure range is 0.09MPa to 0.11MPa.

[0016] Furthermore, based on the comparison result that the mixing homogeneity of the mixed LLZTO is greater than the preset mixing homogeneity, it is determined that the ammonium fluoride and the LLZTO powder without surface treatment are not mixed uniformly under the preset mixing conditions.

[0017] Furthermore, under the condition of determining that the mixing is uneven, it is determined that the mixing rate is increased by a first preset mixing rate adjustment coefficient based on a comparison result that the difference between the mixing homogeneity and the preset mixing homogeneity is less than or equal to the preset difference.

[0018] Furthermore, under the condition of determining that the mixing is uneven, it is determined that the mixing rate is increased by a second preset mixing rate adjustment coefficient based on a comparison result that the difference between the mixing homogeneity and the preset mixing homogeneity is greater than the preset difference.

[0019] Furthermore, based on the comparison result that the reaction deviation index of the LLZTO with the LiF layer covering the surface is greater than the reaction deviation index threshold, it is determined that the side reaction suppression is unqualified.

[0020] Furthermore, under the condition that the reaction suppression is determined to be unqualified, based on the comparison result that the ratio of the reaction deviation index threshold to the reaction deviation index is less than or equal to the preset ratio, it is determined to increase the preset heating rate by the first preset heating rate adjustment coefficient.

[0021] Furthermore, under the condition that the reaction suppression is determined to be unqualified, based on the comparison result that the ratio of the reaction deviation index threshold to the reaction deviation index is greater than the preset ratio, it is determined to increase the preset heating rate by the second preset heating rate adjustment coefficient.

[0022] Compared with the prior art, the present invention has the following beneficial effects: by mixing ammonium fluoride with LLZTO, dynamically adjusting the mixing rate according to the homogeneity of the mixture after mixing, heating to the decomposition temperature and maintaining the constant temperature, cooling and releasing the pressure, and then screening to remove the residue, the heating rate is adjusted based on the reaction deviation index feedback to avoid excessive or insufficient local fluorination, thereby reducing the battery production cost, improving the ionic conductivity, reducing the proportion of electrolyte added to the lithium-ion battery, reducing the lithium ion shuttling rate, and improving the battery energy density.

[0023] Furthermore, ammonium fluoride treatment successfully introduced fluorine elements on the surface of LLZTO, forming a fluorine-containing modified layer, which improved the surface properties of the LLZTO powder. After the modified LLZTO powder was exposed to air for a period of time, the fluorine elements on the surface could have a positive effect on the interfacial properties of the material, thereby improving its application performance in all-solid-state lithium batteries and enhancing the structural stability and good electrochemical properties of LLZTO.

[0024] Furthermore, the present invention determines the uniformity by comparing the mixing homogeneity with a preset threshold through this scheme. When the mixing is uneven, the mixing rate is dynamically increased according to the difference, and the adjustment range is limited by the coefficient to avoid overadjustment, thereby reducing the mixing uniformity error and avoiding powder agglomeration caused by sudden rate changes. At the same time, the mixing efficiency is improved, and the thickness consistency of the LiF coating layer on the LLZTO surface is improved, thereby improving the ionic conductivity.

[0025] Further, the present application determines the side reaction inhibition effect by dynamically evaluating the reaction deviation index, determines unqualified if the index exceeds the threshold value, and adjusts the temperature rising rate based on the ratio of the threshold value to the actual value, reduces the amount of byproduct, improves the ion conductivity of LLZTO, reduces the high temperature rate error based on the threshold ratio, improves the reaction efficiency, avoids local overheating caused by too fast temperature rising, realizes green production, and significantly improves the performance consistency and process reliability of solid electrolyte material.

[0026] Further, the ammonium fluoride surface treatment significantly improves the ion conductivity, verifies the promotion effect of the LiF interface layer on ion transmission, and the conductivity is still lower than the ammonium fluoride treatment group through traditional modification methods such as ball milling, calcination and pickling, the fluorination agent dosage and performance are positively correlated, the ammonium fluoride method has strong process compatibility, and the side reaction is inhibited through the LiF layer. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The flowchart of the preparation method of the lithium battery solid electrolyte of the embodiment of the present application;

[0028] Figure 2 The EDS element map of the LLZTO treated by the ammonium fluoride of the embodiment of the present application exposed in air for 12h;

[0029] Figure 3 The flowchart of determining whether the mixing is uniform or not of the embodiment of the present application;

[0030] Figure 4 The flowchart of determining whether the side reaction inhibition is qualified or not of the embodiment of the present application;

[0031] Figure 5 The XPS spectrum of the LLZTO not treated by the ammonium fluoride of the embodiment of the present application exposed in air for 12h;

[0032] Figure 6 The XPS spectrum of the LLZTO treated by the ammonium fluoride of the embodiment of the present application exposed in air for 12h. DETAILED DESCRIPTION

[0033] In order to make the purpose and advantages of the present application more clear and obvious, the present application is further described below in combination with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the protection scope of the present application.

[0034] The preferred embodiments of the present application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application, and are not used to limit the protection scope of the present application.

[0035] It should be pointed out that the data in this embodiment are obtained by comprehensive analysis and evaluation of the historical test data and the corresponding historical test results of the three months before this test. It can be understood by those skilled in the art that the present invention can determine the above parameters for a single item by selecting the value with the highest proportion as the preset standard parameter based on the data distribution, using weighted summation to use the obtained value as the preset standard parameter, substituting each historical data into a specific formula and using the value obtained by the formula as the preset standard parameter or other selection methods, as long as the present invention can clearly define the different specific situations in the single determination process through the obtained values.

[0036] See also Figure 1 As shown, it is a flow chart of a method for preparing a solid electrolyte for a lithium battery according to an embodiment of the present invention.

[0037] The method for preparing a solid electrolyte for a lithium battery according to an embodiment of the present invention comprises:

[0038] Step S1, mixing ammonium fluoride and LLZTO powder that has not been surface treated at a preset molar ratio under preset mixing conditions to obtain mixed LLZTO;

[0039] Step S2, determining whether the mixing is uniform based on the mixing homogeneity of the mixed LLZTO, and adjusting the mixing rate according to the difference between the mixing homogeneity and a preset mixing homogeneity;

[0040] Step S3, placing the uniformly mixed LLZTO into a reaction container, heating the reaction container to a preset decomposition temperature at a preset heating rate and maintaining the temperature for a preset decomposition time;

[0041] Step S4, screening the LLZTO with a surface covered with a LiF layer obtained after the reaction container is cooled to a preset temperature and released at a preset pressure under inert atmosphere;

[0042] Step S5, determining the eligibility of side reaction suppression based on the reaction deviation index of the LLZTO with the LiF layer on the surface, and adjusting the preset heating rate according to the ratio of the reaction deviation index threshold to the reaction deviation index;

[0043] Step S6: Under the condition that the side reaction is suppressed to a satisfactory level, an LLZTO composite electrolyte is prepared.

[0044] In the embodiment of the present invention, the LLZTO composite electrolyte is a solid electrolyte for lithium batteries, that is, LLZTO powder with a surface covered with a LiF layer and having qualified side reaction suppression.

[0045] Specifically, the present invention mixes ammonium fluoride and LLZTO, dynamically adjusts the mixing rate according to the homogeneity of the mixture, heats the mixture to a decomposition temperature and maintains a constant temperature, cools and releases the pressure, and then screens and removes the residue. The heating rate is adjusted based on the reaction deviation index feedback to avoid local excessive or insufficient fluorination, thereby reducing battery production costs, improving ionic conductivity, reducing the proportion of electrolyte added to lithium-ion batteries, reducing the lithium ion shuttling rate, and improving battery energy density.

[0046] See also Figure 2 As shown, it is an EDS elemental diagram of LLZTO treated with ammonium fluoride according to the present invention and exposed to air for 12 hours.

[0047] EDS images show a clear distribution of fluorine (F) on the LLZTO surface, indicating that the ammonium fluoride treatment successfully introduced fluorine onto the LLZTO surface, forming a fluorine-containing modified layer that improves the surface properties of the LLZTO powder. Compared to untreated LLZTO, the fluorine on the surface of the modified LLZTO powder after exposure to air for a period of time positively impacts the material's interfacial properties, thereby enhancing its performance in all-solid-state lithium batteries. Other elements, such as La, Zr, and Ta, also exhibit a corresponding distribution, and the overall elemental distribution is relatively uniform, which helps maintain the material's structural stability and good electrochemical performance.

[0048] Specifically, in step S1, the preset molar ratio of ammonium fluoride: LLZTO powder is x:1, wherein x is 0.05 to 0.1, preferably 0.075, and the preset mixing conditions include a mixing speed and a mixing time. The mixing speed range is 200 rpm to 500 rpm, preferably 350 rpm, and the mixing time range is 30 min to 60 min, preferably 45 min.

[0049] See also Figure 3 As shown, it is a flow chart of determining whether the mixing is uniform according to an embodiment of the present invention.

[0050] Specifically, the embodiment of the present invention determines whether the mixing is uniform based on the comparison result of the mixing homogeneity of the mixed LLZTO and the preset mixing homogeneity;

[0051] When the mixing homogeneity is less than or equal to the preset mixing homogeneity, it is determined that the mixing is uniform;

[0052] When the mixing homogeneity is greater than the preset mixing homogeneity, it is determined that the mixing is uneven.

[0053] In an embodiment of the present invention, the preset mixing homogeneity is 15%. The preset mixing homogeneity is obtained when the maximum value of the mixing homogeneity of several historical mixing processes is taken. Within the preset conditions such as mixing speed and mixing time, the preset mixing homogeneity can effectively distinguish between uniform and uneven mixing states. However, the above value is not limited to this, and those skilled in the art can also adjust the value according to actual needs.

[0054] During the implementation process, the mixing homogeneity is the percentage of the deviation between the discrete degree of particle size distribution and the actual concentration of ammonium fluoride. The powder particle size distribution is detected in real time by a laser particle size analyzer, and the ammonium fluoride is quantified by EDS (energy spectrum analysis) surface scanning.

[0055] Specifically, in an embodiment of the present invention, under the condition of determining that the mixing is uneven, the mixing rate is adjusted according to a comparison result of the difference between the mixing homogeneity and the preset mixing homogeneity and the preset difference;

[0056] When the difference is less than or equal to the preset difference, it is determined to increase the mixing rate to a corresponding value using a first preset mixing rate adjustment coefficient of 1.03;

[0057] When the difference is greater than the preset difference, it is determined to increase the mixing rate to a corresponding value using a first preset mixing rate adjustment coefficient of 1.07;

[0058] The difference is the difference between the mixing homogeneity and the preset mixing homogeneity.

[0059] In the embodiment of the present invention, the preset difference value is 5%, but the above value is not limited thereto, and those skilled in the art can also adjust the value according to actual needs.

[0060] In an embodiment of the present invention, the increased mixing rate is the product of the preset mixing rate adjustment coefficient and the mixing rate. The preset mixing rate adjustment coefficient includes a first preset mixing rate adjustment coefficient, which has a value of 1.03 and a second preset mixing rate adjustment coefficient, which has a value of 1.07. In order to ensure that the adjusted mixing rate meets actual needs, the adjustment range should not be too large, so the corresponding adjustment coefficient is set to control the adjustment range.

[0061] Specifically, the present invention determines the uniformity by comparing the mixing homogeneity with a preset threshold through this scheme. When the mixing is uneven, the mixing rate is dynamically increased according to the difference, and the adjustment range is limited by the coefficient to avoid overadjustment, thereby reducing the mixing uniformity error and avoiding powder agglomeration caused by sudden rate changes. At the same time, the mixing efficiency is improved, and the thickness consistency of the LiF coating layer on the LLZTO surface is improved, thereby improving the ionic conductivity.

[0062] Specifically, in step S3, the preset heating rate range is 5°C / min~10°C / min, preferably 7°C / min, the preset decomposition temperature range is 180°C~220°C, preferably 200°C, and the preset decomposition time range is 1.2h~1.5h, preferably 1.3h.

[0063] Specifically, in step S4, the preset cooling temperature is 25°C to 30°C, preferably 27°C, and the preset pressure relief pressure range is 0.09MPa to 0.11MPa, preferably 0.1MPa.

[0064] See also Figure 4 As shown, it is a flow chart of determining the eligibility of side reaction inhibition according to an embodiment of the present invention.

[0065] Specifically, the embodiment of the present invention determines the eligibility of the side reaction suppression based on the comparison result of the reaction deviation index of the LLZTO covered with the LiF layer and the reaction deviation index threshold;

[0066] When the reaction deviation index is less than or equal to the reaction deviation index threshold, it is determined that the side reaction inhibition is qualified;

[0067] When the reaction deviation index is greater than the reaction deviation index threshold, it is determined that the side reaction suppression is unqualified.

[0068] In an embodiment of the present invention, the reaction deviation index threshold is 0.82. The reaction deviation index threshold is obtained when the maximum value of the reaction deviation index of several historical side reactions that have qualified for suppression is taken. Within the preset conditions such as the preset heating rate, the preset decomposition temperature, the preset decomposition time, the preset cooling temperature, and the preset pressure relief pressure, the preset mixing homogeneity can effectively distinguish between uniform and uneven mixing states. However, the above values ​​are not limited thereto, and those skilled in the art can also adjust the values ​​according to actual needs.

[0069] During implementation, the reaction deviation index is the product of the normalized value of the by-product ammonia concentration and the concentration weight of 0.6 and the normalized value of the crystal phase structure change rate and the change rate weight of 0.4. The by-product ammonia concentration is monitored by a mass spectrometer, and the degree of lattice distortion is analyzed by XRD (X-ray diffraction). The normalized value of the ammonia concentration is the ratio of the measured ammonia concentration to the preset safety concentration, and the preset safety concentration is the historical maximum allowable concentration. The normalized value of the crystal phase structure change rate is the ratio of the lattice distortion rate to the preset distortion threshold, and the preset distortion threshold is the critical value of LLZTO lattice collapse.

[0070] Specifically, in an embodiment of the present invention, when it is determined that the side reaction suppression is unqualified, the preset heating rate is adjusted according to the comparison result of the ratio of the reaction deviation index threshold to the reaction deviation index and the preset ratio;

[0071] When the ratio is less than or equal to the preset ratio, it is determined to increase the preset heating rate to a corresponding value using a first preset heating rate adjustment coefficient of 1.05;

[0072] When the ratio is greater than the preset ratio, it is determined to increase the preset heating rate to a corresponding value using a second preset heating rate adjustment coefficient of 1.09;

[0073] The ratio is the ratio of the reaction deviation index threshold to the reaction deviation index.

[0074] In the embodiment of the present invention, the preset ratio is 0.25, but the above value is not limited thereto, and those skilled in the art may also adjust the value according to actual needs.

[0075] In an embodiment of the present invention, the increased preset heating rate is the product of the preset heating rate adjustment coefficient and the preset heating rate. The preset heating rate adjustment coefficient includes a first preset heating rate adjustment coefficient, which is 1.05, and a second preset heating rate adjustment coefficient, which is 1.09. In order to ensure that the adjusted preset heating rate meets actual needs, the adjustment range should not be too large, so the corresponding adjustment coefficient is set to control the adjustment range.

[0076] Specifically, the present invention determines the side reaction inhibition effect by dynamically evaluating the reaction deviation index. If the index exceeds the threshold, it is judged to be unqualified, and the heating rate is adaptively adjusted based on the ratio of the threshold value to the actual value, thereby reducing the amount of by-products generated and improving the LLZTO ion conductivity. The graded heating adjustment based on the threshold ratio reduces the high-temperature rate error, improves the reaction efficiency, avoids local overheating caused by excessive heating, and realizes green production at the same time, significantly improving the performance consistency and process reliability of solid electrolyte materials.

[0077] See also Figures 5-6 As shown, Figure 5 This is the XPS spectrum of LLZTO without ammonium fluoride treatment after exposure to air for 12 hours. Figure 6 This is the XPS spectrum of LLZTO treated with ammonium fluoride in an embodiment of the present invention after being exposed to air for 12 hours.

[0078] Specifically, in order to determine whether the LLZTO surface contains lithium carbonate, the embodiment of the present invention uses XPS (X-ray photoelectron spectroscopy) to analyze the surface of the LLZTO. Figure 5 In comparison, Figure 6 The absence of C1s (electrons filling the first energy level s orbital of carbon) spectrum proves that no Li2CO3 is generated on the LLZTO surface treated with ammonium fluoride after exposure to air for 12 h. Figure 6 compared to Figure 5The most significant difference is the appearance of the F1s peak, which indicates that the ammonium fluoride treatment successfully introduced fluorine onto the LLZTO surface. This demonstrates that the embodiments of the present invention effectively introduced fluorine onto the material surface.

[0079] Example 1: Step S1, ammonium fluoride material and unsurface-treated LLZTO powder are uniformly mixed at a molar ratio of 0.05:1, the mixture is heated to a decomposition temperature and kept warm, and then naturally cooled and depressurized to obtain LLZTO powder with a surface covered with a LiF layer;

[0080] Step S2, exposing the LLZTO powder treated with ammonium fluoride to air for 12 hours to obtain dry LLZTO;

[0081] Step S3, the dried LLZTO and PVDF-HFP are transferred into N,N-dimethylformamide (DMF) in a mass ratio of 8:2 to obtain a mixed solution, the mixed solution is placed in a water bath at 60° C., and magnetically stirred for 6 hours to obtain a uniformly dispersed slurry;

[0082] Step S4: Transfer the evenly dispersed slurry to a flat and clean glass plate with uniform thickness, control the thickness of the electrolyte film by adjusting the height of the scraper, place the prepared electrolyte slurry in a vacuum oven, and dry it at 60°C for 24 hours to obtain a composite electrolyte film;

[0083] Step S5, cutting the composite electrolyte film into discs, and assembling a stainless steel / composite electrolyte / stainless steel battery, lithium sheet / composite electrolyte / lithium sheet symmetrical battery in the manner of button cell assembly;

[0084] In step S6, the ionic conductivity δ of the symmetrical battery obtained in step S4 can be calculated by the equation: where d is the thickness of the electrolyte membrane, R is the measured resistance value, and S is the contact area between the composite electrolyte film and the stainless steel electrode. The symmetrical battery is subjected to constant current charge and discharge cycles.

[0085] In Example 1, the mixing speed is 350 rpm, the mixing time is 45 min, the preset heating rate is 7°C / min, the preset decomposition temperature is 200°C, the preset decomposition time is 1.3 h, the preset cooling temperature is 27°C, and the preset pressure relief pressure is 0.1 MPa.

[0086] In this embodiment, the thickness of the electrolyte membrane is 200 μm, the measured resistance value is 80 Ω, and the diameter of the stainless steel electrode is 16 mm. Inputting the above parameters into the calculation formula of ionic conductivity, we can obtain δ=1.3×10 -4 S / cm -1 The Li2CO3 removal efficiency was calculated to be 90% by XPS analysis of the C 1s peak and the F 1s peak.

[0087] Example 2: Step S1, ammonium fluoride material and unsurface-treated LLZTO powder are uniformly mixed at a molar ratio of 0.1:1, the mixture is heated to a decomposition temperature and kept warm, and then naturally cooled and depressurized to obtain LLZTO powder with a surface covered with a LiF layer;

[0088] Step S2, exposing the LLZTO powder treated with ammonium fluoride to air for 12 hours to obtain dry LLZTO;

[0089] Step S3, the dried LLZTO and PVDF-HFP are transferred into N,N-dimethylformamide (DMF) in a mass ratio of 8:2 to obtain a mixed solution, the mixed solution is placed in a water bath at 60° C., and magnetically stirred for 6 hours to obtain a uniformly dispersed slurry;

[0090] Step S4: Transfer the evenly dispersed slurry to a flat and clean glass plate with uniform thickness, control the thickness of the electrolyte film by adjusting the height of the scraper, place the prepared electrolyte slurry in a vacuum oven, and dry it at 60°C for 24 hours to obtain a composite electrolyte film;

[0091] Step S5, cutting the composite electrolyte film into discs, and assembling a stainless steel / composite electrolyte / stainless steel battery, lithium sheet / composite electrolyte / lithium sheet symmetrical battery in the manner of button cell assembly;

[0092] In step S6, the ionic conductivity δ of the symmetrical battery obtained in step S4 can be calculated by the equation: where d is the thickness of the electrolyte membrane, R is the measured resistance value, and S is the contact area between the composite electrolyte film and the stainless steel electrode. The symmetrical battery is subjected to constant current charge and discharge cycles.

[0093] In Example 2, the mixing speed is 350 rpm, the mixing time is 45 min, the preset heating rate is 7°C / min, the preset decomposition temperature is 200°C, the preset decomposition time is 1.3 h, the preset cooling temperature is 27°C, and the preset pressure relief pressure is 0.1 MPa.

[0094] In this embodiment, the thickness of the electrolyte membrane is 200 μm, the measured resistance value is 35.5Ω, and the diameter of the stainless steel electrode is 16 mm. Inputting the above parameters into the calculation formula of ionic conductivity, we can obtain δ=2.8×10 -4 S / cm -1 The Li2CO3 removal efficiency was calculated to be 95% by XPS analysis of the C 1s peak and the F 1s peak.

[0095] Example 3: Except for the reaction conditions, the rest are the same as in Example 1.

[0096] In Example 3, the mixing speed is 200 rpm, the mixing time is 30 min, the preset heating rate is 5°C / min, the preset decomposition temperature is 180°C, the preset decomposition time is 1.2 h, the preset cooling temperature is 25°C, and the preset pressure relief pressure is 0.09 MPa.

[0097] In this embodiment, the thickness of the electrolyte membrane is 200 μm, the measured resistance value is 105Ω, and the diameter of the stainless steel electrode is 16 mm. Inputting the above parameters into the calculation formula of ionic conductivity, we can obtain δ=1.0×10 -4 S / cm -1 The Li2CO3 removal efficiency was calculated to be 88% by XPS analysis of the C 1s peak and the F 1s peak.

[0098] Example 4: Except for the reaction conditions, the rest are the same as in Example 1.

[0099] In Example 4, the mixing speed is 500 rpm, the mixing time is 60 min, the preset heating rate is 10°C / min, the preset decomposition temperature is 200°C, the preset decomposition time is 1.5 h, the preset cooling temperature is 30°C, and the preset pressure relief pressure is 0.11 MPa.

[0100] In this embodiment, the thickness of the electrolyte membrane is 200 μm, the measured resistance value is 42 Ω, and the diameter of the stainless steel electrode is 16 mm. Inputting the above parameters into the calculation formula of ionic conductivity, we can obtain δ=3.0×10 -4 S / cm -1 The Li2CO3 removal efficiency was calculated to be 92% by XPS analysis of the C 1s peak and the F 1s peak.

[0101] Comparative Example 1:

[0102] Step S1, exposing LLZTO powder that has not been treated with ammonium fluoride to air for 12 hours to obtain dry LLZTO;

[0103] Step S2, the dried LLZTO and PVDF-HFP are transferred into N,N-dimethylformamide (DMF) in a mass ratio of 8:2 to obtain a mixed solution, the mixed solution is placed in a water bath at 60° C., and magnetically stirred for 6 hours to obtain a uniformly dispersed slurry;

[0104] Step S3: Transfer the evenly dispersed slurry to a flat and clean glass plate with uniform thickness, control the thickness of the electrolyte film by adjusting the height of the scraper, place the prepared electrolyte slurry in a vacuum oven, and dry it at 60°C for 24 hours to obtain a composite electrolyte film;

[0105] Step S4, cutting the composite electrolyte film into discs, and assembling a stainless steel / composite electrolyte / stainless steel battery, lithium sheet / composite electrolyte / lithium sheet symmetrical battery in the manner of button cell assembly;

[0106] In step S5, the ionic conductivity δ of the symmetrical battery obtained in step S4 can be calculated by the equation: where d is the thickness of the electrolyte membrane, R is the measured resistance value, and S is the contact area between the composite electrolyte film and the stainless steel electrode. The symmetrical battery is subjected to constant current charge and discharge cycles.

[0107] In this embodiment, the thickness of the electrolyte membrane is 200 μm, the measured resistance value is 4522 Ω, and the diameter of the stainless steel electrode is 16 mm. Inputting the above parameters into the calculation formula of ionic conductivity, we can obtain δ=2.2×10 -6 S / cm -1 , the C 1s peak and F 1s peak were analyzed by XPS to calculate the Li2CO3 removal rate to be 0%.

[0108] Comparative Example 2:

[0109] Step S1, placing LLZTO powder that has not been treated with ammonium fluoride in a ball mill, adding anhydrous ethanol as a dispersion medium, ball milling at a speed of 300 rpm for 6 hours, and then exposing it to air for 12 hours to obtain dry LLZTO;

[0110] Step S2, the dried LLZTO and PVDF-HFP are transferred into N,N-dimethylformamide (DMF) in a mass ratio of 8:2 to obtain a mixed solution, the mixed solution is placed in a water bath at 60° C., and magnetically stirred for 6 hours to obtain a uniformly dispersed slurry;

[0111] Step S3: Transfer the evenly dispersed slurry to a flat and clean glass plate with uniform thickness, control the thickness of the electrolyte film by adjusting the height of the scraper, place the prepared electrolyte slurry in a vacuum oven, and dry it at 60°C for 24 hours to obtain a composite electrolyte film;

[0112] Step S4, cutting the composite electrolyte film into discs, and assembling a stainless steel / composite electrolyte / stainless steel battery, lithium sheet / composite electrolyte / lithium sheet symmetrical battery in the manner of button cell assembly;

[0113] In step S5, the ionic conductivity δ of the symmetrical battery obtained in step S4 can be calculated by the equation: where d is the thickness of the electrolyte membrane, R is the measured resistance value, and S is the contact area between the composite electrolyte film and the stainless steel electrode. The symmetrical battery is subjected to constant current charge and discharge cycles.

[0114] In the present embodiment, the thickness of the electrolyte film is 200 μm, the measured resistance value is 199 Ω, the diameter of the stainless steel electrode is 16 mm, and the above parameters are input into the calculation formula of the ionic conductivity to obtain δ = 0.5 x 10 -4 S / cm -1 The C 1s peak and the F 1s peak are analyzed by XPS to calculate the Li2CO3 removal rate as 20%.

[0115] Comparative Example 3:

[0116] Step S1, the LLZTO powder without ammonium fluoride treatment is placed in a tube furnace, heated to 600℃ at a rate of 5℃ / min, calcined in an air atmosphere for 4 hours, and after natural cooling, placed in air for 12h to obtain dry LLZTO;

[0117] Step S2, the dry LLZTO and PVDF-HFP are moved into N,N-dimethylformamide (DMF) according to a mass ratio of 8:2 to obtain a mixed solution, and the mixed solution is placed in a water bath at 60℃, and a uniformly dispersed slurry is obtained after magnetic stirring for 6h;

[0118] Step S3, the uniformly dispersed slurry is transferred to a glass plate with uniform thickness and flat and clean, the thickness of the electrolyte film is controlled by adjusting the height of the scraper, and the prepared electrolyte slurry is placed in a vacuum oven for drying treatment at a temperature of 60℃ for 24h to obtain a composite electrolyte film;

[0119] Step S4, the composite electrolyte film is cut into a round piece, and a stainless steel / composite electrolyte / stainless steel battery and a lithium sheet / composite electrolyte / lithium sheet symmetric battery are assembled according to the assembly method of the button cell;

[0120] Step S5, the ionic conductivity δ of the symmetric battery obtained in step S4 can be calculated by the equation: δ = d / S R, wherein d is the thickness of the electrolyte film, R is the measured resistance value, and S is the contact area between the composite electrolyte film and the stainless steel electrode. The symmetric battery is subjected to constant current charge and discharge cycles.

[0121] In the present embodiment, the thickness of the electrolyte film is 200 μm, the measured resistance value is 110 Ω, the diameter of the stainless steel electrode is 16 mm, and the above parameters are input into the calculation formula of the ionic conductivity to obtain δ = 0.9 x 10 -4 S / cm -1 The C 1s peak and the F 1s peak are analyzed by XPS to calculate the Li2CO3 removal rate as 40%.

[0122] Comparative Example 4:

[0123] Step S1, immersing the LLZTO powder that has not been treated with ammonium fluoride in a 0.1M HCl solution, stirring for 2 hours, washing with deionized water until neutral, and then exposing it to air for 12 hours to obtain dry LLZTO;

[0124] Step S2, the dried LLZTO and PVDF-HFP are transferred into N,N-dimethylformamide (DMF) in a mass ratio of 8:2 to obtain a mixed solution, the mixed solution is placed in a water bath at 60° C., and magnetically stirred for 6 hours to obtain a uniformly dispersed slurry;

[0125] Step S3: Transfer the evenly dispersed slurry to a flat and clean glass plate with uniform thickness, control the thickness of the electrolyte film by adjusting the height of the scraper, place the prepared electrolyte slurry in a vacuum oven, and dry it at 60°C for 24 hours to obtain a composite electrolyte film;

[0126] Step S4, cutting the composite electrolyte film into discs, and assembling a stainless steel / composite electrolyte / stainless steel battery, lithium sheet / composite electrolyte / lithium sheet symmetrical battery in the manner of button cell assembly;

[0127] In step S5, the ionic conductivity δ of the symmetrical battery obtained in step S4 can be calculated by the equation: where d is the thickness of the electrolyte membrane, R is the measured resistance value, and S is the contact area between the composite electrolyte film and the stainless steel electrode. The symmetrical battery is subjected to constant current charge and discharge cycles.

[0128] In this embodiment, the thickness of the electrolyte membrane is 200 μm, the measured resistance value is 83 Ω, and the diameter of the stainless steel electrode is 16 mm. Inputting the above parameters into the calculation formula of ionic conductivity, we can obtain δ=1.1×10 -4 S / cm -1 The Li2CO3 removal efficiency was calculated to be 70% by XPS analysis of the C 1s peak and the F 1s peak.

[0129] Table 1 Resistance value and ionic conductivity test results,

[0130]

[0131] The data in the table show that ammonium fluoride surface treatment significantly improves ionic conductivity. Examples 1-2 are 2 to 3 orders of magnitude higher than Comparative Example 1, verifying the promoting effect of the LiF interface layer on ion transport. Comparative Examples 2-4, through traditional modification methods such as ball milling / calcination / acid washing, still have lower conductivity than the ammonium fluoride treatment group, proving the uniqueness of ammonium fluoride in-situ reaction in optimizing the interface properties of LLZTO. Traditional methods, such as Comparative Examples 2, 3, and 4, cannot efficiently remove Li2CO3. Example 2 uses a higher ammonium fluoride ratio, and the conductivity reaches the optimal value of 2.8×10 -4The specific conductivity of the fluorinated material is 0. 1 S / cm, indicating that the amount of fluorination agent is positively correlated with the performance; the ammonium fluoride method has strong process compatibility and inhibits side reactions through the LiF layer.

[0132] The technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the present application, and the technical solutions after the changes or replacements will fall within the protection scope of the present application.

[0133] The above description is only for the preferred embodiments of the present application and is not intended to limit the present application; for those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a solid electrolyte for a lithium battery, characterized in that: include: Mixing ammonium fluoride and LLZTO powder that has not been surface treated at a preset molar ratio under preset mixing conditions to obtain mixed LLZTO; determining whether the mixing is uniform based on the mixing homogeneity of the mixed LLZTO, and adjusting the mixing rate according to the difference between the mixing homogeneity and a preset mixing homogeneity; Based on the comparison result that the mixing homogeneity of the mixed LLZTO is greater than the preset mixing homogeneity, it is determined that the ammonium fluoride and the LLZTO powder without surface treatment are not mixed uniformly under the preset mixing conditions; Under the condition that the mixing is determined to be uneven, determining to increase the mixing rate by a first preset mixing rate adjustment coefficient based on a comparison result that a difference between the mixing homogeneity and the preset mixing homogeneity is less than or equal to a preset difference; Under the condition that the mixing is determined to be uneven, determining to increase the mixing rate by a second preset mixing rate adjustment coefficient based on a comparison result that a difference between the mixing homogeneity and the preset mixing homogeneity is greater than a preset difference; The mixing homogeneity is the percentage of the deviation between the discrete degree of particle size distribution and the actual concentration of ammonium fluoride. The powder particle size distribution is detected in real time by a laser particle size analyzer, and the ammonium fluoride is quantified by EDS (energy dispersive spectrum analysis) surface scanning; The uniformly mixed LLZTO is placed in a reaction container, and the reaction temperature of the reaction container is increased to a preset decomposition temperature at a preset heating rate and then maintained for a preset decomposition time; Screening the LLZTO with a surface covered with a LiF layer obtained after the reaction container is cooled to a preset temperature and released at a preset pressure under inert atmosphere; Determining the eligibility of side reaction suppression based on the reaction deviation index of the LLZTO having the LiF layer on the surface, and adjusting the preset heating rate according to the ratio of the reaction deviation index threshold to the reaction deviation index; Determining that the side reaction inhibition is unqualified based on a comparison result that the reaction deviation index of the LLZTO covered with the LiF layer is greater than a reaction deviation index threshold; Under the condition that the reaction suppression is determined to be unqualified, determining to increase the preset heating rate by a first preset heating rate adjustment coefficient based on a comparison result that the ratio of the reaction deviation index threshold to the reaction deviation index is less than or equal to the preset ratio; Under the condition that the reaction suppression is determined to be unqualified, determining to increase the preset heating rate by a second preset heating rate adjustment coefficient based on a comparison result that a ratio of the reaction deviation index threshold to the reaction deviation index is greater than a preset ratio; The reaction deviation index is the product of the normalized value of the byproduct ammonia concentration and the concentration weight of 0.6, and the normalized value of the crystal phase structure change rate and the change rate weight of 0.

4. The byproduct ammonia concentration is monitored by a mass spectrometer, and the degree of lattice distortion is analyzed by XRD (X-ray diffraction). The normalized value of the ammonia concentration is the ratio of the measured ammonia concentration to the preset safety concentration, where the preset safety concentration is the historical maximum allowable concentration. The normalized value of the crystal phase structure change rate is the ratio of the lattice distortion rate to the preset distortion threshold, where the preset distortion threshold is the critical value of LLZTO lattice collapse. Under the condition that the side reaction is suppressed to a qualified level, the LLZTO composite electrolyte is prepared.

2. The method for preparing a solid electrolyte for lithium batteries according to claim 1, wherein: The preset molar ratio is ammonium fluoride: LLZTO powder is x:1, and x is 0.05 to 0.

1. The preset mixing conditions include a mixing speed and a mixing time. The mixing speed range is 200 rpm to 500 rpm, and the mixing time range is 30 min to 60 min.

3. The method for preparing a solid electrolyte for lithium batteries according to claim 1, wherein: The preset heating rate range is 5°C / min to 10°C / min, the preset decomposition temperature range is 180°C to 220°C, and the preset decomposition time range is 1.2h to 1.5h.

4. The method for preparing a solid electrolyte for lithium batteries according to claim 1, wherein: The preset cooling temperature is 25°C to 30°C, and the preset pressure relief pressure range is 0.09MPa to 0.11MPa.

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